Torrefaction, a thermal pretreatment process, is gaining attention as it improves the physical properties and chemical composition of biomass for recycling. During torrefaction, biomass is heated slowly in an inert or oxygen-deficit environment to a maximum temperature of 300°C. The torrefaction process creates a solid uniform product with lower moisture and higher energy content than the raw biomass. During torrefaction, moisture and some volatile organic compounds volatilize from the biomass. Depending on stoichiometry and other conditions, non-condensable gas species, including CO and CO₂, are formed. The specific objectives of this research are to: 1) understand the impact of torrefaction on product quality in terms of the physical properties, chemical composition, and storage behavior of the biomass; 2) discuss the various reactors used for biomass torrefaction; and 3) develop a model for designing a moving bed torrefier, considering fundamental heat and mass transfer calculations. Torrefaction improves the physical properties, chemical composition, and energy and storage properties of biomass. Torrefaction of biomass at 300°C increases the energy content by about 30% as compared to the raw biomass. For example, when torrefied, the calorific value of the biomass increases from about 18–19 MJ/kg to about 20–24 MJ/kg. The torrefied material has a moisture content of about 1–3% wet basis (w.b.). The loss of the hydroxyl group during torrefaction makes the biomass hydrophobic. The brittle nature of the torrefied biomass makes it easier to grind. The devolatilization and carbonization reactions change the proximate and ultimate composition. The carbon content increases, whereas the hydrogen, oxygen, and nitrogen content of the biomass decreases. Despite its superior properties, the commercialization of torrefaction technology is slow due to challenges associated with reactor design and final product quality. The different types of reactors that are typically used for biomass torrefaction are the fixed bed, rotary drum, microwave, fluidized bed, and horizontal and vertical moving bed. The moving bed reactor has gained popularity among the different torrefaction reactor designs as it is easy to operate and scale. In addition, it helps produce a uniform torrefied product. In this paper, different moving bed torrefaction and gas recycle concepts are conceptualized to assess the features, advantages, and disadvantages of various design and operating concepts. These designs include example concepts for: 1) vertical and horizontal torrefaction reactors; 2) recycle of all or a portion of the torrefier off-gas; 3) counter and co-flowing gas and biomass in the torrefier; 4) controls for the system temperatures, pressures, flow rates, and gas compositions; and 5) the ability to sample the biomass feed, torrefied product, and gas streams for analysis as needed to investigate the thermal decomposition, physical behavior, and operational performance of the torrefaction system. The article also briefly describes the solid feed system, gas supply and recycle system, solid product management, torrefier gas monitoring, control system, and fugitive dust emissions control. The model presented in this paper includes a set of equations for basic calculations to configure the torrefaction reactor dimensions, such as diameter and height of the moving bed torrefier for different capacities based on target and calculated solids and gas velocities, residence times, and temperatures.

烘焙是一种热预处理过程，因为它改善了用于回收的生物质的物理特性和化学成分，因此越来越受到关注。在烘焙过程中，生物质在惰性或缺氧环境中被缓慢加热到 300°C 的最高温度。烘焙过程创造了一种固体均匀的产品，与原始生物质相比，其水分含量更低，能量含量更高。在烘焙过程中，水分和一些挥发性有机化合物会从生物质中挥发。根据化学计量和其他条件，不可凝气体种类，包括 CO 和 CO ₂， 形成。本研究的具体目标是： 1) 从生物质的物理特性、化学成分和储存行为方面了解烘焙对产品质量的影响；2) 讨论用于生物质烘焙的各种反应器；3) 开发用于设计移动床干燥机的模型，考虑基本的传热和传质计算。烘焙改善了生物质的物理特性、化学成分以及能量和存储特性。与原始生物质相比，生物质在 300°C 下的烘焙使能量含量增加了约 30%。例如，当烘焙时，生物质的热值从大约 18-19 MJ/kg 增加到大约 20-24 MJ/kg。烘焙材料的水分含量约为 1-3% 湿基 (wb)。烘焙过程中羟基的损失使生物质疏水。烘焙生物质的脆性使其更容易研磨。脱挥发分和碳化反应改变了近似和最终组成。碳含量增加，而生物质的氢、氧和氮含量减少。尽管具有优异的性能，但由于与反应器设计和最终产品质量相关的挑战，烘焙技术的商业化进展缓慢。通常用于生物质烘焙的不同类型的反应器是固定床、转鼓、微波、流化床以及水平和垂直移动床。移动床反应器在不同的烘焙反应器设计中很受欢迎，因为它易于操作和扩展。此外，它有助于生产均匀的烘焙产品。在本文中，不同的移动床烘焙和气体循环概念被概念化，以评估各种设计和操作概念的特征、优点和缺点。这些设计包括以下示例概念：1) 立式和卧式烘焙反应器；2) 回收全部或部分烘干机废气；3) 在干燥机中逆流和共流的气体和生物质；4) 系统温度、压力、流量和气体成分的控制；5) 能够根据需要对生物质进料、烘焙产品和气流进行采样以进行分析，以研究烘焙系统的热分解、物理行为和操作性能。文章还简要介绍了固体进料系统、供气和循环系统，固体产品管理、烘干机气体监测、控制系统和扬尘排放控制。本文中提出的模型包括一组用于配置烘焙反应器尺寸的基本计算方程，例如基于目标和计算出的固体和气体速度、停留时间和温度的不同容量的移动床干燥器的直径和高度。